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1 | // (C) Copyright 2009-2011 Frederic Bron, Robert Stewart, Steven Watanabe & Roman Perepelitsa. |
2 | // | |
3 | // Use, modification and distribution are subject to the Boost Software License, | |
4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
5 | // http://www.boost.org/LICENSE_1_0.txt). | |
6 | // | |
7 | // See http://www.boost.org/libs/type_traits for most recent version including documentation. | |
8 | ||
9 | #include <boost/config.hpp> | |
10 | #include <boost/type_traits/detail/yes_no_type.hpp> | |
11 | #include <boost/type_traits/integral_constant.hpp> | |
12 | #include <boost/type_traits/is_const.hpp> | |
13 | #include <boost/type_traits/is_fundamental.hpp> | |
14 | #include <boost/type_traits/is_pointer.hpp> | |
15 | #include <boost/type_traits/is_same.hpp> | |
16 | #include <boost/type_traits/is_void.hpp> | |
17 | #include <boost/type_traits/remove_cv.hpp> | |
18 | #include <boost/type_traits/remove_pointer.hpp> | |
19 | #include <boost/type_traits/remove_reference.hpp> | |
20 | ||
21 | // avoid warnings | |
22 | #if defined(__GNUC__) | |
23 | # pragma GCC system_header | |
24 | #elif defined(BOOST_MSVC) | |
25 | # pragma warning ( push ) | |
26 | # pragma warning ( disable : 4244 4913) | |
27 | # if BOOST_WORKAROUND(BOOST_MSVC_FULL_VER, >= 140050000) | |
28 | # pragma warning ( disable : 6334) | |
29 | # endif | |
30 | #endif | |
31 | ||
32 | namespace boost { | |
33 | namespace detail { | |
34 | ||
35 | // This namespace ensures that argument-dependent name lookup does not mess things up. | |
36 | namespace BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl) { | |
37 | ||
38 | // 1. a function to have an instance of type T without requiring T to be default | |
39 | // constructible | |
40 | template <typename T> T &make(); | |
41 | ||
42 | ||
43 | // 2. we provide our operator definition for types that do not have one already | |
44 | ||
45 | // a type returned from operator BOOST_TT_TRAIT_OP when no such operator is | |
46 | // found in the type's own namespace (our own operator is used) so that we have | |
47 | // a means to know that our operator was used | |
48 | struct no_operator { }; | |
49 | ||
50 | // this class allows implicit conversions and makes the following operator | |
51 | // definition less-preferred than any other such operators that might be found | |
52 | // via argument-dependent name lookup | |
53 | struct any { template <class T> any(T const&); }; | |
54 | ||
55 | // when operator BOOST_TT_TRAIT_OP is not available, this one is used | |
56 | no_operator operator BOOST_TT_TRAIT_OP (const any&, int); | |
57 | ||
58 | ||
59 | // 3. checks if the operator returns void or not | |
60 | // conditions: Lhs!=void | |
61 | ||
62 | // we first redefine "operator," so that we have no compilation error if | |
63 | // operator BOOST_TT_TRAIT_OP returns void and we can use the return type of | |
64 | // (lhs BOOST_TT_TRAIT_OP, returns_void_t()) to deduce if | |
65 | // operator BOOST_TT_TRAIT_OP returns void or not: | |
66 | // - operator BOOST_TT_TRAIT_OP returns void -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns returns_void_t | |
67 | // - operator BOOST_TT_TRAIT_OP returns !=void -> (lhs BOOST_TT_TRAIT_OP, returns_void_t()) returns int | |
68 | struct returns_void_t { }; | |
69 | template <typename T> int operator,(const T&, returns_void_t); | |
70 | template <typename T> int operator,(const volatile T&, returns_void_t); | |
71 | ||
72 | // this intermediate trait has member value of type bool: | |
73 | // - value==true -> operator BOOST_TT_TRAIT_OP returns void | |
74 | // - value==false -> operator BOOST_TT_TRAIT_OP does not return void | |
75 | template < typename Lhs > | |
76 | struct operator_returns_void { | |
77 | // overloads of function returns_void make the difference | |
78 | // yes_type and no_type have different size by construction | |
79 | static ::boost::type_traits::yes_type returns_void(returns_void_t); | |
80 | static ::boost::type_traits::no_type returns_void(int); | |
81 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(::boost::type_traits::yes_type)==sizeof(returns_void((make<Lhs>() BOOST_TT_TRAIT_OP,returns_void_t()))))); | |
82 | }; | |
83 | ||
84 | ||
85 | // 4. checks if the return type is Ret or Ret==dont_care | |
86 | // conditions: Lhs!=void | |
87 | ||
88 | struct dont_care { }; | |
89 | ||
90 | template < typename Lhs, typename Ret, bool Returns_void > | |
91 | struct operator_returns_Ret; | |
92 | ||
93 | template < typename Lhs > | |
94 | struct operator_returns_Ret < Lhs, dont_care, true > { | |
95 | BOOST_STATIC_CONSTANT(bool, value = true); | |
96 | }; | |
97 | ||
98 | template < typename Lhs > | |
99 | struct operator_returns_Ret < Lhs, dont_care, false > { | |
100 | BOOST_STATIC_CONSTANT(bool, value = true); | |
101 | }; | |
102 | ||
103 | template < typename Lhs > | |
104 | struct operator_returns_Ret < Lhs, void, true > { | |
105 | BOOST_STATIC_CONSTANT(bool, value = true); | |
106 | }; | |
107 | ||
108 | template < typename Lhs > | |
109 | struct operator_returns_Ret < Lhs, void, false > { | |
110 | BOOST_STATIC_CONSTANT(bool, value = false); | |
111 | }; | |
112 | ||
113 | template < typename Lhs, typename Ret > | |
114 | struct operator_returns_Ret < Lhs, Ret, true > { | |
115 | BOOST_STATIC_CONSTANT(bool, value = false); | |
116 | }; | |
117 | ||
118 | // otherwise checks if it is convertible to Ret using the sizeof trick | |
119 | // based on overload resolution | |
120 | // condition: Ret!=void and Ret!=dont_care and the operator does not return void | |
121 | template < typename Lhs, typename Ret > | |
122 | struct operator_returns_Ret < Lhs, Ret, false > { | |
123 | static ::boost::type_traits::yes_type is_convertible_to_Ret(Ret); // this version is preferred for types convertible to Ret | |
124 | static ::boost::type_traits::no_type is_convertible_to_Ret(...); // this version is used otherwise | |
125 | ||
126 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(is_convertible_to_Ret(make<Lhs>() BOOST_TT_TRAIT_OP))==sizeof(::boost::type_traits::yes_type))); | |
127 | }; | |
128 | ||
129 | ||
130 | // 5. checks for operator existence | |
131 | // condition: Lhs!=void | |
132 | ||
133 | // checks if our definition of operator BOOST_TT_TRAIT_OP is used or an other | |
134 | // existing one; | |
135 | // this is done with redefinition of "operator," that returns no_operator or has_operator | |
136 | struct has_operator { }; | |
137 | no_operator operator,(no_operator, has_operator); | |
138 | ||
139 | template < typename Lhs > | |
140 | struct operator_exists { | |
141 | static ::boost::type_traits::yes_type s_check(has_operator); // this version is preferred when operator exists | |
142 | static ::boost::type_traits::no_type s_check(no_operator); // this version is used otherwise | |
143 | ||
144 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(s_check(((make<Lhs>() BOOST_TT_TRAIT_OP),make<has_operator>())))==sizeof(::boost::type_traits::yes_type))); | |
145 | }; | |
146 | ||
147 | ||
148 | // 6. main trait: to avoid any compilation error, this class behaves | |
149 | // differently when operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the | |
150 | // standard. | |
151 | // Forbidden_if is a bool that is: | |
152 | // - true when the operator BOOST_TT_TRAIT_OP(Lhs) is forbidden by the standard | |
153 | // (would yield compilation error if used) | |
154 | // - false otherwise | |
155 | template < typename Lhs, typename Ret, bool Forbidden_if > | |
156 | struct trait_impl1; | |
157 | ||
158 | template < typename Lhs, typename Ret > | |
159 | struct trait_impl1 < Lhs, Ret, true > { | |
160 | BOOST_STATIC_CONSTANT(bool, value = false); | |
161 | }; | |
162 | ||
163 | template < typename Lhs, typename Ret > | |
164 | struct trait_impl1 < Lhs, Ret, false > { | |
165 | BOOST_STATIC_CONSTANT(bool, | |
166 | value = (operator_exists < Lhs >::value && operator_returns_Ret < Lhs, Ret, operator_returns_void < Lhs >::value >::value)); | |
167 | }; | |
168 | ||
169 | // specialization needs to be declared for the special void case | |
170 | template < typename Ret > | |
171 | struct trait_impl1 < void, Ret, false > { | |
172 | BOOST_STATIC_CONSTANT(bool, value = false); | |
173 | }; | |
174 | ||
175 | // defines some typedef for convenience | |
176 | template < typename Lhs, typename Ret > | |
177 | struct trait_impl { | |
178 | typedef typename ::boost::remove_reference<Lhs>::type Lhs_noref; | |
179 | typedef typename ::boost::remove_cv<Lhs_noref>::type Lhs_nocv; | |
180 | typedef typename ::boost::remove_cv< typename ::boost::remove_reference< typename ::boost::remove_pointer<Lhs_noref>::type >::type >::type Lhs_noptr; | |
181 | BOOST_STATIC_CONSTANT(bool, value = (trait_impl1 < Lhs_noref, Ret, BOOST_TT_FORBIDDEN_IF >::value)); | |
182 | }; | |
183 | ||
184 | } // namespace impl | |
185 | } // namespace detail | |
186 | ||
187 | // this is the accessible definition of the trait to end user | |
188 | template <class Lhs, class Ret=::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME,_impl)::dont_care> | |
189 | struct BOOST_TT_TRAIT_NAME : public integral_constant<bool, (::boost::detail::BOOST_JOIN(BOOST_TT_TRAIT_NAME, _impl)::trait_impl< Lhs, Ret >::value)>{}; | |
190 | ||
191 | } // namespace boost | |
192 | ||
193 | #if defined(BOOST_MSVC) | |
194 | # pragma warning ( pop ) | |
195 | #endif |